An example of the conventional flow rate measurement device of this kind is disclosed in Unexamined Japanese Patent Publication No. 2002-71421.
Gas meters include a gas flow meter and are interposed in gas supply lines entering residential buildings. The conventional gas meter achieves different billing schemes for respective gas appliances in such a manner that a plurality of integrators are connected to the gas meter which function separately to calculate a volumetric sum of gas flowing during a predetermined time zone and a volumetric sum of flows which fall within a specific flow range. That is, volumetric sums of gas flows are separately calculated according to different time zones and different flow ranges and used to bill under the different billing schemes.
An example of the billing scheme will be described with reference to FIG. 13. At least one discount consumption threshold and at least one discount time zone are prescribed in advance. A discount rate is applied to a volume of gas which has been consumed above the discount consumption threshold and within the discount time zone. For example, the shadowed areas of gas consumption shown in FIG. 13 are subject to discount. However, this method falls short of identifying gas appliances used and thus cannot provide a billing statement transparent to customers so as to conveniently identify rates billed in connection with specific gas appliances. On the other hand, Japanese Patent Application No. 2003-149027, for example, discloses a method of identifying a particular gas appliance.
The operation of a flow rate measurement device of this kind will be described with reference to FIG. 14. FIG. 14 shows a profile of gas consumption exhibited by a gas appliance during the beginning of the consumption thereby and reference values (a profile table) for use in determining profile matching. For a single gas appliance, as many profile tables are prepared as the consumption profiles the single gas appliance is to exhibit under the different combustion controls performed on the gas appliance. In addition, these profile tables are prepared for each of the gas appliances used in a household. In use, these profile tables are looked up to search for one profile which matches the flow profile actually measured by the flow rate measuring device of the gas meter and thereby identify the gas appliance being in use.
In the conventional method as discussed above, however, a plurality of profiles have to be prepared for identifying a single gas appliance. Therefore, when many gas appliances are subject to identification, a number of tables will have to be prepared, and a search for the matching profile will be prolonged. Hence, the apparatus for use in identification will become expensive. So will the gas meter itself. In addition, in order to identify a plurality of gas appliances being used simultaneously, the profile tales have to be prepared for all possible combinations of gas appliances. The number of the combinations may sometimes be enormous. The conventional method is therefore flawed in that it cannot provide a practical solution to identifying a plurality of appliances.